Thanks to all for your informative and encouraging responses. I was basically afraid to tackle the valves and cam chain, but after finding some step by step instructions on adjusting the cam chain I thought that even I could do that. Took the time today to do that today and low and behold it worked. 80% of the clattering is now gone! AND, it runs better. Feels like it is more comfortable cruising at 62-65 now, whereas before it felt comfortable at 52-55.
So, I know it's no big deal to you mechanics, but it's a milestone for me.
Thanks for everyone's encouragement.